All eukaryotic cells share the ability to sense and respond to sudden changes in their environment. The mechanisms by which cells protect themselves against damage caused by stress conditions have both medical and agricultural implications. Many of the genetic pathways regulating the cellular stress response have been conserved from simple eukaryotes like S. cerevisiae to humans. Most studies on stress have focused on signal transduction pathways that communicate changes in the external environment to the nucleus, where changes in gene expression are triggered. In comparison to these transcriptional responses, relatively little is known about stress signaling to or from the translational apparatus. We have identified a small ankyrin-repeat protein, Yarl, with a role in the S. cerevisiae stress response. Cells deleted for YARI are sensitive to low and high temperature stress, and to osmotic and oxidative stress. deltayar1 cells are also sensitive to the protein synthesis inhibitor anisomycin. In fission yeast and mammals, anisomycin is a potent activator of a "ribotoxic" stress signal that is believed to originate in arrested ribosomes and leads to stress MAPK activation. Using yeast two-hybrid analysis, we identified three potential protein partners for YarI, including RpS3, a ribosomal protein, and the product of LTV1 (for low temperature viability), deletion of which results in sensitivity to low temperature and osmotic stress. The physical interaction between Yarl and RpS3 is supported by evidence of a genetic interaction. We propose to investigate in detail the role of Yarl in the stress response. Our research plan has three specific aims: (1) Investigate genetic and biochemical interactions between Yarl and its partners; (2) Determine the function of the Yarl:RpS3 interaction; and (3) Conduct genetic screens to determine where YARI functions relative to known stress response genes. The proposed project is highly likely to yield new mechanistic insights into how yeast cells respond to stress.